The present invention relates to a method and a system for testing a cathode ray tube (CRT) or like products such as a cathode ray tube monitor. [Note: here the term "cathode ray tube monitor" means a dismantled monitor, i.e. the housing of the monitor is removed for testing purpose, leaving the assembly of its CRT, control circuit and the bezel of the screen. The present invention is mainly directed to the testing of CRT monitor. However, for the sake of simplicity, both CRT and CRT monitor are hereinafter generally referred to as "CRT".]
The cathode ray tube of a television or a monitor, after finished in its production line, must be tested and adjusted to correct its various geometrical and optical deviations and distorsions. The test and adjustment of geometrical deviations, for example, mainly relied upon physical labor in the past, wherein a standard test pattern, which is generally a chessboard-like lattice, namely "crosshatch", formed by m vertical lines and n horizontal lines (m and n are positive integers, preferably odd numbers and can be equal to each other, for example, a 5.times.5 latticework formed by 5 vertical and 5 horizontal lines) are produced on the screen of a monitor to be tested. The distances between the individual intersecting points (used as reference points) are measured by physical labor to obtain the deviations of the actual values of the geometrical parameters from the nominal values thereof and to adjust and to correct these parameters. In the recent few years, it was suggested to use an electronic camera instead of the human eyes to read the standard test pattern from the screen and input the data into a computer for processing to obtain the geometrical deviations of a tested CRT. An example is disclosed in a co-pending U.S. patent application Ser. No. 08/059,779, of the applicant. (See FIG. 10). When an electronic camera is used to read the relative position of the reference points of a standard figure on a screen, the margins of the screen (i.e. the border lines of the screen and the frame of a monitor) are practically used as baseline to facilitate the locating of the center of the screen. The bezel is read at first, then the standard test pattern is read, thus locating the center of the screen and thereby obtaining the actual positions (coordinates) of the reference points of the standard test pattern on the screen (hereinafter referred to as "ACTUAL S-Mn"). The nominal positions of the reference points (hereinafter referred to as "NOMINAL S-Mn") were previously stored in the computer. A comparison between the actual positions and the nominal position is performed to obtain the geometrical deviations of the CRT, which can then be displayed for an operator to make manual adjustment or correction, or alternatively (in the case of automatic adjustment) directly be transmitted to an automatic adjusting device to make automatic adjustment or correction. [NOTE: In the above known technique involving electronic cameras, there are some known systems which use not merely a single electronic camera, but a plurality of (for example three or four) electronic cameras, each responsible for only a respective zone of a screen. For example, the first, second, third and fourth cameras respectively read the upper right, lower right, lower left, and upper left quarters (zones) of the screen. The reason for the use of more than one electronic camera is that the resolution of an electronic camera may not be high enough to sufficiently resolve all the tiny pixels of a screen. In principle, however, these cameras works similarly as a single-camera system. The respective reading of divided zones of a screen by a plurality of electronic cameras is similar to the compound eyes of a fly. Thus the known system with a plurality of electronic cameras is hereinafter referred to as "compound eye system", in contrast to a "single eye system" which uses a single electronic camera to read a whole screen.]
In the known technique, when reading a screen using an electronic camera or more electronic cameras, it is necessary to accurately fix the position of the electronic camera relative to the screen. For this reason, in the known single-eye or compound eye systems, mechanical adjusting/positioning means are provided to position and to fix a tested screen relative to the electronic camera in all directions X, Y and Z. Such mechanical means occupies a considerable portion in the volume, weight, and energy consumption of the system. The mechanical positioning procedure also occupies a considerable portion of the time of a test cycle. Moreover, the mechanical positioning means must rigidly touch the frame of the screen during the test, thus causing uncomfortable noises and suffering the risk of the damage of the products. These disadvantages are inevitable in all the currently used systems and not yet overcome.
To solve this problem, the mechanical positioning which involves concrete contact with the frame of the screen must be replaced by a contactless method, using intangible softwares to locate the screen. In so doing, the mass, the volume, the energy and time consumption of the system can be greatly saved.
If the conventional contact-type mechanical positioning is abandoned, the electronic camera can no longer be accurately positioned relative to the screen. Since the visual field of an electronic camera is a two-dimensional planar projection, it cannot accurately evaluate the three dimensional (3D) coordinate of a screen which is not positioned in predetermined relationship to the camera, but randomly situated. In the conventional system, owing to the mechanical positioning means, the camera always reads only one kind of planar projection. Once the positioning means is abandoned, the camera will read different projections from different angles. For the conventional single eye or compound eye system, it is impossible to accurately locate a screen without mechanical positioning means.
According to the present invention, this problem is solved by using at least two, and preferably three electronic cameras to respectively read the whole screen from different angles. (The assembly of these electronic cameras will be hereinafter referred to as "electronic camera assembly".) Just as two eyes can evaluate the distance of an object from the optical angle, two electronic camera can accurately locate a screen from the different planar projections they read. Since the position (3D-coordinate) of the electronic camera assembly can be known (if it is fixed in a definite site), the position (3D-coordinate) of the screen can be known. Then a standard test pattern can be produced on the screen, which is then read to obtain the actual positions of its reference points relative to the screen. [NOTE: In reading the standard figure, a single electronic camera will be enough to obtain the actual positions of its reference points, since the accurate position of the screen has been known.] Since both the position of the screen and the position of the standard test pattern are known, the actual positions of the reference points relative to the screen ("ACTUAL S-Mn") can be known. Then the data can be compared with the nominal positions of reference points ("NOMINAL S-Mn") to obtain the deviations, using conventional methods.
A system to realize the method of this invention comprises an assembly of at least two electronic cameras for this purpose. The output of each electronic camera is connected to a computer. In order that the computer can execute the method of this invention, the system further comprises the corresponding data and softwares required for the execution of the method, which can be installed in the computer in form of modules.
It is known to use two electronic cameras to measure the dimensions of an object (generally known as "stereo vision"). Although the "stereo vision" technique was discussed in some publications, it has never been utilized in testing a screen.
Besides, it is noteworthy that there are a certain differences between the test of a screen and the measurement of ordinary objects. A point P of an ordinary object (for example, a workpiece) always appears optically the same to an electronic camera however the object is rotated, i.e. from whatever angle. The image of the point P is directly read into the camera without any refraction. But this is not the case for a screen. A bright point on the screen is produced by the bombardment of an electronic beam on the fluorescent coating on the backside of the glass panel of a screen. The bright point is read not directly, but through the glass panel, into the electronic camera. Thus the refraction of its image may vary with different reading angles of the electronic camera. The refractive factor as a function of the angle of the electronic camera had better be taken into consideration to obtain the highest accuracy of the read data. As for the details of the correction of such refractive factor, the modern computer software technique can sufficiently deal with it.
Theoretically, two electronic cameras are enough for "stereo vision". But the stereoscopic detection will be still better if an additional third electronic camera is used. It is proved that the rate of poor test is greatly reduced if three instead of two electronic cameras are used.
In the known "stereo vision" technique, the two electronic cameras must be fixed relative to each other, and the internal and external parameters of their lenses must be corrected, before the cameras can be used for measurement. Likewise, in the system according to this invention, the three electronic camera must be fixed on a carrier board prior to their use in testing CRT, and like correction must be performed. Then the carrier board together with the electronic cameras is mounted as a whole onto the system for use.
The system according to this invention, with its two or more electronic cameras which offer a stereoscopic sight, is hereinafter referred to as "stereoscopic (or 3D) plural eye system".
When electronic camera/cameras is/are used to read a screen (in whatever system, the conventional single-eye system, the compound-eye system, or the 3D plural-eye system of this invention), the margin of the screen is often used to facilitate the reading and the locating of the center of the screen. To locate the margin, the frame (or in technical terminology "bezel") of the screen must be read. Unlike the optically active screen, the bezel is not self-glowing. Hence an additional light source must be used to illuminate the optically passive bezel to enable the electronic camera to read it. In the aforesaid co-pending U.S. patent application, an annular fluorescent tube (FL) serves as the light source. Moreover, in the conventional systems, the electronic camera works in a dark box, thus there is no risk of the disturbance of exotic light. In the present invention, such a dark box is absent. In order to isolated the camera from foreign lights, a dark curtain can be used. The additional light source for the present invention must be such that a reflected beam from the glass panel of the screen never reaches the electronic cameras. For this purposes, the light source preferably illuminates the bezel from a very low incident angle.
The principle of this invention has been clearly stated hereinbefore. In the following are the further details of a preferred embodiment of this invention, illustrated in connection with the accompanying drawing in which: